The present invention relates to a monolayered, biaxially stretch-oriented and heat-set tubular packaging casing, in particular to a synthetic sausage casing, based on polyamide.
Packaging casings of the type specified above are in most cases produced from polymer mixtures, in order to compensate for certain disadvantageous properties of polyamide. Thus, it is known, for example, to use a mixture comprising polyamide and polyester as a material for sausage casings (EP-A-0,176,980). It has been found, however, that casings of this type are relatively turbid and exhibit an unnatural gloss. It is true that clear casings can be produced from pure polyamide, but these casings have the disadvantage that their permeability to steam is higher than that of comparable casings made of polyamide blends. Moreover, these casings are not suited for the production of large-diameter sausages due to their elastic properties.
Furthermore, a three-layered polyamide casing has been disclosed, which is composed of a central layer comprising a copolyamide with units of hexamethylene diamine, isophthalic acid and terephthalic acid, and two top layers of polyethylene (EP-A-0 305 959). However, this film is not clear due to the PE top layers. It also requires a relatively complicated production process due to its three-layered design.